In general, in vehicle engines, engine overheating or reduction of friction between various mechanisms may be prevented by circulating an engine oil, and to this end, an oil pump is adopted.
However, the oil pump is operated so as to discharge an oil flow toward a discharge side and suction an oil flow returned toward a suction side, and thus, when the oil pump is in operation, the driving torque of an engine cannot help being lost.
In vehicles, improvement of engine driving torque is an indispensable condition for improving fuel efficiency. Therefore, the driving torque loss which is horsepower consumed to deliver oil due to an oil pump and is proportional to the product of flow rate and oil pressure of the oil pump can be reduced by improving the performance of the oil pump.
Recently, the importance of saving fuel in vehicles have further been growing due to global high price of oil and carbon dioxide restriction, and thus, in development of vehicles, improvement of fuel efficiency and environment friendliness have been considered as a core issue.
In particular, considering that the improvement of engine driving torque is indispensable for improvement of fuel efficiency, reduction of driving torque loss due to an oil pump may be very effective for improvement of fuel efficiency.
For example, as illustrated in FIG. 1, a structure for improving fuel efficiency by bypassing a portion of oil through a relief valve at a high rpm and thereby lowering the pressure of oil has been disclosed.
However, the oil pump as described above might alleviate oil pressure within a high-speed range, but the oil pressure in a middle-speed range was still maintained high, and therefore, there was a limitation of decreasing the efficiency of improving fuel consumption.
[Related Art Document]
Korean Patent No. 10-1509994 (Registered on Apr. 1, 2015)